1. Field of the Invention
The invention relates to a method and apparatus for control of a lamp. Specifically, the invention is directed to a method and apparatus for controlling a vehicle headlight that uses a single light source (such as a metal halide discharge lamp, etc.) and that is equipped with a beam-type switching device for switching between high beam and low beam.
2. Discussion of the Related Art
FIG. 7 shows an example of the construction of a related art type headlamp 90. This headlamp 90 is equipped with a light source base 91, which has a fulcrum 91a. A single light source 92 attached to light source base 91 has a lumination source 92a. A solenoid 93 is provided at the tip of the opposite side of fulcrum 91a of light source base 91. Beam-type switching is carried out by activating solenoid 93 and shifting the lumination source 92a relative to reflector 94 from a low beam position to a high beam position.
The solenoid 93 must maintain lumination source 92a in the high beam position during the time period in which the vehicle is driven in the high beam position. It is anticipated that the application of operational electrical power to the solenoid 93 will occur continuously for a rather long time period, for example, during lengthy travel on a high-speed highway. Lumination source 92a returns from the high beam position to the low beam position upon deactivation of the solenoid 93.
However, the solenoid 93 utilized by the related art headlight 90 requires comparatively high electrical power at the start of movement from the low beam position to the high beam position since plunger 93b is distant from solenoid body 93a at the start of movement.
Although sufficient electrical power is supplied to begin movement of solenoid 93, as explained previously, this same electrical power is then continuously applied during the time that the vehicle is driven while using the high beam. Therefore excessive heating due to the continuous application of a great deal of electrical power to solenoid 93 occurs and a large-scale size solenoid 93 is necessary to avoid overheating. The related art headlight results in problems to be solved such as higher cost, increased weight, overheating, malfunctioning, etc.